screenshot
Possible causes:__The Junction may already have been buggy (see other bug)
__Black magic (never underestimate black magic when working with computers, or in general, but especially when working with computers)
Additional info:
__testing shows that it also happens when not underneath a driving train.
__It does not matter in which direction you drag / place the rail.
__Error only occurs when placing that exact piece of rail, placing any other rail works fine.
__It only happens just before the train stops (see other bug), adding way before that or after that does not give an error.
____This may mean that this would be an easy way to see when the junction becomes buggy: if you can add the rail, it is not buggy yet.
Edit: original error was in 0.14.02, still happens in 0.14.03